Ceramic capacitors are also called ceramic capacitors or monolithic capacitors. As the name implies, ceramic capacitors are capacitors whose dielectric material is ceramic. According to different ceramic materials, it can be divided into two types: low-frequency ceramic capacitors and high-frequency ceramic capacitors. According to the classification of structure, it can be divided into disc capacitors, tubular capacitors, rectangular capacitors, chip capacitors, feedthrough capacitors, etc.
Introduction
Its shape is mostly sheet, and there are also tubular, round and other shapes.
Ceramic capacitors are a general term for capacitors with ceramic materials as the medium. There are many varieties, and the dimensions vary greatly. According to the voltage used, it can be divided into high-voltage, medium-voltage and low-voltage ceramic capacitors. According to the temperature coefficient, the dielectric constant can be divided into negative temperature coefficient, positive temperature coefficient, zero temperature coefficient, high dielectric constant, low dielectric constant, etc. In addition, there are classification methods of type I, type II and type III. Compared with other capacitors, general ceramic capacitors have the advantages of high operating temperature, large specific capacity, good moisture resistance, small dielectric loss, and the temperature coefficient of capacitance can be selected in a wide range. Widely used in electronic circuits, the amount is very considerable.
Classification and characteristics of ceramic capacitors
1. Semiconductor ceramic capacitors
The miniaturization of capacitors means that capacitors can obtain as much capacity as possible in as small a volume as possible, which is one of the trends in the development of capacitors. For separation capacitor components, there are two basic approaches to miniaturization, that is, to increase the dielectric constant of the dielectric material as much as possible and to reduce the thickness of the dielectric layer as much as possible.
Among ceramic materials, the dielectric constant of ferroelectric ceramics is very high, but when using ferroelectric ceramics to make ordinary ferroelectric ceramic capacitors, it is difficult to make the ceramic dielectric very thin. First of all, due to the low strength of ferroelectric ceramics, it is easy to break when it is thin, and it is difficult to carry out actual production operations. Secondly, when the ceramic medium is very thin, it is easy to cause various structural defects, and the production process is very difficult.
The surface layer ceramic capacitor uses a very thin insulating layer formed on the surface of semiconductor ceramics such as BaTiO3 as the dielectric layer, and the semiconductor ceramic itself can be regarded as a series circuit of the dielectric. The thickness of the insulating surface layer of surface layer ceramic capacitors fluctuates between 0.01 and 100 μm depending on the formation method and conditions. This not only utilizes the high dielectric constant of ferroelectric ceramics, but also effectively reduces the thickness of the dielectric layer, which is an effective solution for preparing micro-miniature ceramic capacitors.
2. Grain boundary layer ceramic capacitors
On the surface of BaTiO3 semiconductor ceramics with relatively well-developed grains, coat appropriate metal oxides (such as CuO or Cu2O, MnO2, Bi2O3, Tl2O3, etc.), and conduct heat treatment under oxidizing conditions at an appropriate temperature. The substance will form a low eutectic solution phase with BaTiO3, rapidly diffuse and penetrate into the interior of the ceramic along the open pores and grain boundaries, and form a thin solid solution insulating layer on the grain boundaries. The resistivity of this thin solid solution insulating layer is very high (up to 1012-1013Ω·cm). Although the interior of the ceramic grain is still a semiconductor, the entire ceramic body exhibits an apparent dielectric constant as high as 2×104 to 8× 104 insulator dielectric. The capacitors prepared with this kind of porcelain are called boundary layer ceramic capacitors (boundarg layer ceramic capacitors), referred to as BL capacitors.
3. High voltage ceramic capacitor
With the rapid development of the electronics industry, it is urgent to develop high-voltage ceramic capacitors with high breakdown voltage, low loss, small size and high reliability. Over the past 20 years, the high-voltage ceramic capacitors successfully developed at home and abroad have been widely used in power systems, laser power supplies, video tape recorders, color TVs, electron microscopes, copiers, office automation equipment, aerospace, missiles, and navigation.
Barium titanate-based ceramic materials have the advantages of high dielectric coefficient and good AC withstand voltage characteristics, but they also have the disadvantages of capacitance change rate increasing with medium temperature and insulation resistance decreasing. The Curie temperature of strontium titanate crystal is -250°C, and it has a cubic perovskite structure at room temperature. It is a paraelectric body and there is no spontaneous polarization. The dielectric coefficient of strontium titanate-based ceramic materials is Small change, tgδ and capacitance change rate are small, these advantages make it very beneficial as a high-voltage capacitor medium.
4. Multilayer ceramic capacitors
Multilayer ceramic capacitors (Multilayer Ceramic Capacitor, MLCC) is the most widely used type of chip components, it is the internal electrode material and the ceramic body in multiple layers alternately stacked in parallel, and co-fired as a whole, also known as Chip monolithic capacitors have the characteristics of small size, high specific capacity, and high precision. They can be mounted on printed circuit boards (PCBs) and hybrid integrated circuit (HIC) substrates, effectively reducing the size of electronic information terminal products (especially Portable product) volume and weight, improve product reliability. It conforms to the development direction of IT industry’s miniaturization, light weight, high performance and multi-function.
Precautions for the use of ceramic capacitors
1. The ceramic capacitor shell is damaged
Ceramic capacitors with damaged shells are prone to leakage current. When the leakage current is too large, a large amount of heat will be emitted to increase the temperature. The temperature rises to a certain extent and burns the circuit, causing a fire.
When using ceramic capacitors, the ceramic capacitors will be checked first. If there are cracks or impurities on the ceramic capacitors, do not use the ceramic capacitors, and replace them with new ceramic capacitors with undamaged shells.
2. Working environment temperature
Normally, the working temperature range of ceramic capacitors is -25°C ~ +85°C, and the working environment temperature should be confirmed before using ceramic capacitors. If the working environment temperature is too low, it will have little effect on ceramic capacitors, but attention should be paid to avoid dew condensation on ceramic capacitors, which will reduce the working performance.
If the temperature is too high, the current surge is too large, the capacity of the ceramic capacitor will decrease, and the working time of the ceramic capacitor will be shortened. Change to a working environment with suitable temperature and ventilation, or add a radiator or electric fan when the ceramic capacitor is working to reduce the temperature to ensure the normal operation of the ceramic capacitor.
3. Working voltage
Before using ceramic capacitors, it should be noted that the working voltage in the circuit cannot exceed the rated voltage of ceramic capacitors. Exceeding the rated voltage will easily lead to short-circuit failure of the ceramic capacitor, and the electronic product will not work normally. It is necessary to replace the ceramic capacitor with a rated voltage higher than the working voltage to ensure the normal operation of the circuit.
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